Studies have been made of ageing effects, both at room temperature and at 125C, on the microstructure of 6040 tinlead solders. A comparison was made of the effect of ageing on slow and rapidly cooled matrices. Precipitation of tin within lead dendrites was observed to occur very rapidly after solidification of the alloy. Subsequently the precipitates coarsened markedly over a period of a few weeks. The matrix of the alloy also coarsened at room temperature over this period. At elevated temperatures a similar sequence of events occurred, but substantially faster. The microstructural origins of the known loss in mechanical strength of solders with ageing are discussed.
Soldering & Surface Mount Technology – Emerald Publishing
Published: Jan 1, 1991